This invention relates generally to printing processes and more particularly to an improved printer registration process.
The design of packaging for goods, principally, consumer goods, has become increasingly more complex in view of the greater number of types of packages available, the wider range of materials from which packages may be made as well as the properties of the goods to be packaged. A package design must consider how the goods are to be safely transported through distribution channels, presented to the consumer at the retail level and handled by the consumer prior to use. In addition, the package graphics or images are important in attracting the attention of the potential purchaser as well as providing the highest quality presentation of the goods to the consumer. Therefore, it is a common practice to provide high quality package "comp", that is, a color comprehensive or mock-up, of the final package so that it may be perceived as accurately as possible in its final form. Further, since the package comp is not designed for actual use, but simply to visually evaluate the package image, it is desirable to provide the highest quality images on the package material at the least cost.
It is impractical to run a small quantity of packages on the automated printing press line used to manufacture the package on a commercial scale. Therefore, most often, such comps are produced by hand. For purposes of this document, the application of interest are those package comps made of a flexible material in which printing processes that print on flexible substrates are used. Often, a drum-type, large format digital printer is used. Such a printer produces a high quality simulation of the package images.
Package comp designs often specify colors that are identified with respect to a chart of standard colors, for example, a "PANTONE" chart commercially available from Pantone Inc. of Moonachie, N.J. However, not all of those "PANTONE" colors can be reproduced or printed using the digital printer. The digital printer is only capable of printing process colors, that is, those colors that can be produced using the colors in the printer print heads which most often are cyan, magenta, yellow and black. It is generally most efficient to print all of the colors on the package comp with the digital printer, and therefore, every effort is made to provide process colors on the digital printer that match the colors specified in the package design. However, white and a number of "PANTONE" colors, for example, gold, etc., cannot be suitably matched with a process color. In those situations, line colors are used which are generally produced by mixing inks to the desired color. Therefore, in producing such a package comp, it would be desirable to use another printing process to apply the line color in combination with the digital printing process which applies the process color.
In such a process, using a computer workstation, a component or line color digital image file is produced that represents a desired line color portion of the package image, for example, a white or gold, that is not printed with the digital printer. Using that component digital image file, the line color is applied to a package substrate using a conventional printing process, such as a silk screen, printing, offset printing or a direct imaging process. The package substrate having the line color image printed with a conventional printing process must then be mounted on the digital printer with which the remainder of the package image, that is, the process color image, will be printed.
As will be appreciated, any attempts to mount the package substrate on the printer drum utilizing known alignment techniques will not result in the process color image being printed in exact alignment with the previously printed line color image. The known mounting techniques suggest that the substrate be aligned utilizing either the physical edges of the printer drum or alignment guide lines that are printed along the edges of the substrate and thus, outside the printed image itself. As will be appreciated, successfully aligning the edges of the substrate or mutually perpendicular guide lines with the printer drum on do not necessarily result in an alignment of the conventionally printed line color image with a superimposed digitally printed image. Such misalignment while not great, it is sufficient to distort the visual perception of the image on the package comp. Thus, the package comp is of insufficient quality to accurately represent the appearance of a high quality, mass produced package.
Therefore, currently, only a trial and error process can be used to mount the flexible substrate on the drum of the digital printer, and such trial and error process is time consuming, inefficient and often requires several attempts before an acceptable package comp is produced. Thus, there are no known alignment techniques for easily, efficiently and reliably mounting a conventionally printed flexible substrate on the drum of the digital printer, so that the line color image matches the process color image that is printed with the digital printer.
In addition, if a silk screening printing process is used, the silk screen may stretch slightly during the screening step; and hence, the silk screened line color image on the packaging substrate no longer matches or corresponds exactly with the component digital image file from which the silk screen was created. Further, packaging material requirements now often specify that the package be made from a material that stretches, for example, polyethylene. With a stretchable material, if the line color image is applied by a silk screening process, both the stretchable material and the silk screen are physically and unsymmetrically stretched with the screening step. Consequently, the silk screened image is even further distorted with respect to the component digital image file from which the silk screen was created.
Consequently, there is a need for an alignment or registration system by which a flexible substrate having a first image printed thereon on at a first location can be precisely mounted on a drum of a digital printer at a different location.